Plesk admin receives emails with the message "452 4.3.1 Insufficient system storage"

Symptoms

Many messages like these are sent to Plesk administrator's email

Out: 220 example.com ESMTP Postfix
In: MAIL From:server@example.com
Out: 452 4.3.1 Insufficient system storage
In: RCPT To:admin@example.com
Out: 503 5.5.1 Error: need MAIL command

Cause

Plesk server is out of storage

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/ploop12525p1 9.8G 9.8G 0G 100% /

Resolution

Increase the storage and extend the partition, or free up space with the options below.

Note: Partitioning is an administrative task; contact your hosting provider for assistance.

• Find directories and files that take the most space and remove some
• Remove Plesk backup files that are no longer needed
• Clean up temporary Plesk files
• Remove large domain logs